The present invention relates to a process for introducing perforations into plastic sheeting and/or plastic or rubber coated sheet materials. More particularly, it relates to a process for introducing perforations into plastic sheeting and/or plastic or rubber coated sheet materials by the use of electricity.
Processes for introducing perforations into plastic sheeting and/or plastic or rubber coated sheet materials of the above mentioned general type are known in the art. Plastic sheeting and plastics or rubber coated textiles, such as artificial leather or waterproofed clothing, have the advantage of being absolutely waterproof. However, they have the disadvantage of either having little or no capabilities for breathing. For various practical applications, such as in the clothing industry, such materials are required to have a certain degree of water vapor permeability while simultaneously having a high degree of water proofness. The water vapor permeability chiefly depends on the number and absolute size of the perforations per unit of surface area.
The German Published patent application (DE-OS) No. 28 30 326 discloses an arrangement for making the fine perforations in sheet-like materials with the aid of high voltage pulses. These high voltage pulses provide uniform and dense perforations. The perforations comply with the standard specifications by maintaining smallest perforation hole diameter which provides both sufficient breathing and a high degree of water proofing of the perforated material.
There are, however, quite a number of materials which are processed into sheeting or used as laminated sheets, such as polyethylene, polypropylene, and natural and synthetic rubber. These materials have a high dielectric constant and therefore make the use of electricity, aided by high-voltage pulses, for creating the perforations impossible. However, in individual cases, by increasing the voltage applied, it is possible to achieve a puncturing or piercing of the material. The resulting holes are as a rule so large that waterproofing can not be provided. The same problem arises from a certain sheet or layer thickness of the material which would be suitable for the electric perforation.